German Published Patent Application No. 101 38 110 describes a signal processing device and a control unit for cooperating with a signal processing device, the signal processing device being designed for processing knocking signals of an internal combustion engine. The signal processing device has a filter which processes the knocking signals of the internal combustion engine. The control unit provides control information which influences the properties of the filter. In particular, the frequency of a pass range of the filter may be influenced.